Conventional in-board marine propulsion systems tend to occupy excessive space inside the vessels—typically encroaching on the decks, cockpit, load bay or other useful spaces. The geometry with which different engines can be installed in different vessels to provide optimum use of space varies, but in order to accommodate different engine orientations, different drives are required and the need to provide different drives for matching different engines with different vessels results in additional costs.
The present invention seeks to provide a marine propulsion system that is compact and that can accommodate engines in various space saving configurations.
While there is a need to keep marine propulsion systems compact, it is advantageous for the vessel's handling and for control over trim adjustments if the moment arm for trim adjustments is relatively long and the present invention seeks to provide a compact marine drive with an increased trimming moment.
Most marine propulsion systems extending from the stern of a vessel includes a drive shaft extending downwards and transmitting motive power to a horizontal propeller shaft. The orientation of the drive shaft is typically vertical and the transmission between the drive shaft and propeller shaft typically includes a reversing clutch, comprising counter-rotating bevel gears that are engaged with the drive shaft and that can engage, in turn, with the propeller shaft. This gear set (or alternative arrangement) needs to be housed in a housing of a lower unit of the drive and the housing typically includes a horizontally orientated widened part extending around the propeller shaft, commonly referred to as a “bullet”.
The bullet and the vertical part of the casing extending above it, need to be wide enough to house the drive shaft and components for transmitting power to the propeller shaft, as well as the bearings for these components and cooling and lubrication arrangements and the casing needs to be strong enough to bear the loads imposed by these internal components. The net result is that the lower units tent to be bulky, causing drag.
The present invention seeks to provide a marine propulsion system with a compact transmission between its drive shaft and propeller shaft and consequently a more compact and hydrodynamic lower unit of the drive.